Fixing device

Abstract

A fixing device includes a fixing roller; a heating unit, a pressing unit, a force imparting mechanism, a first pressure releasing mechanism including a first cam portion actable on the force imparting mechanism and a first gear portion for driving the first cam portion; and a second pressure releasing mechanism including a second cam portion actable on the force imparting mechanism and a second gear portion for driving the second cam portion. The first gear portion and the second gear portion engage with each other, and a driving force is transmitted from one gear portion of the first and second gear portions to the other gear portion.

What is claimed is: 
     
       1. A fixing device comprising:
 a fixing roller; 
 a heating unit for forming a heating nip in cooperation with said fixing roller; 
 a pressing unit for forming a fixing nip in cooperation with said fixing roller; 
 a force imparting mechanism for imparting a force to said heating unit and said pressing unit in directions of sandwiching said fixing roller; 
 a first pressure releasing mechanism including a first cam portion actable on said force imparting mechanism in a direction of spacing said heating unit from said fixing roller and including a first gear portion for driving said first cam portion; and 
 a second pressure releasing mechanism including a second cam portion actable on said force imparting mechanism in a direction of spacing said pressing unit from said fixing roller and including a second gear portion for driving said second cam portion, 
 wherein said first gear portion and said second gear portion engage with each other, and a driving force is transmitted from one gear portion of said first and second gear portions to the other gear portion of said first and second gear portions. 
 
     
     
       2. A fixing device according to  claim 1 , wherein a part of one of said first and second gear portions with respect to a circumferential direction is provided with a recessed portion where a pitch between adjacent teeth is broader than another pitch with respect to the circumferential direction of said one of said first and second gear portions, and a part of the other of said first and second gear portions with respect to the circumferential direction is provided with a projected portion capable of entering only the recessed portion of said one of said first and second gear portions with respect to the circumferential direction. 
     
     
       3. A fixing device according to  claim 2 , wherein the projected portion enters the recessed portion at a timing other than a period in which said heating unit and said pressing unit move in a direction of being spaced from said fixing roller by action of said first and second cam portions on said force imparting mechanism. 
     
     
       4. A fixing device according to  claim 2 , wherein the projected portion enters the recessed portion at a timing when maximum outer diameter portions of said first and second cam portions act on said force imparting mechanism. 
     
     
       5. A fixing device according to  claim 2 , wherein the projected portion enters the recessed portion at a timing when said first and second cam portions do not act on said force imparting mechanism. 
     
     
       6. A fixing device according to  claim 1 , wherein said heating unit includes a cylindrical film contacting said fixing roller and a heater, contacting an inner surface of said film, for forming the heating nip between said film and said fixing roller in cooperation with said fixing roller. 
     
     
       7. A fixing device according to  claim 1 , wherein said pressing unit includes a cylindrical film contacting said fixing roller and a sliding member, contacting an inner surface of said film, for forming the fixing nip between said film and said fixing roller in cooperation with said fixing roller.